Aluminum-silicon alloy



Patented 9, 19 26. a a a ourrao STAT 1,572,488 PATENT tori-Tics.

ZAY JEFFRIEB, OI SHAKER HEIGHTS, AND ROBERT B. ARCHER, 01 LAKEWOOD,OHIO,

ASSIGNOBS TO LLUKIHUI 001mm OF AMERICA, PITTSBURGH, PENNSYL- VAN 1A, ACORPORATION 01' PEHHSYLVANIA.

Lam-saloon annoy.

No Drawing. priginal application fled January 4, 1921, Serial R0.485,024. Divided and this applica- To all whom it may cmwernzz Be itknown that we, ZAY Jmnms, of

Shaker Heights, and ROBERT S. Aaomm, of Lakewood, both in the county ofCuyahoga 5 and State of Ohio, have invented certain new and usefulImprovements in Aluminum-Silicon Alloys, of which the following is afull, clear, and exact description.

The invention y 'hirh forms the subject of our present a plu tion (adivision of our copcnding apphcat on Serial -N 'o. 435,024, filedJanuary 4, 1921, now patent No. 1,508, 556, issued September 16, 1924)relates to the production of aluminum alloy castings, particularlycastings made of alloys containing silicon or copper or both, with orwithout other metals, and its chief object is to provide a simple andefl'ective method which will produce light-weight castings with ahitherto unobtainable combination of physical properties, especially asregards elastic limit, tensile strength and ductility. 'Do this andother ends the invention consists in the novel method and producthereinafter described.

As will be seen from the subjoined descri tion, the invention isbasedupon the com ination of certain steps, some of them novel with us,and in part the invention resides in the discovery that certain alloysare especially susceptib e to improvement by heat treatment aftercasting, and that certain methods of casting such alloys further andpeculiarly adapt them to such treat-.

3 ment; and in the additional discovery of temperature and duration ofheat treatment in combinations appropriate to the particular alloys andmethod of casting involved.

With the aid of these discoveries we have 4 been able to producecastings having improved physical properties with respect to elasticlimit, tensile strength and ductility to an extent hithertounattainable, with the result that it is now possible to use aluminumalloy castings fpr purposes for which their use has previously eenimpracticable. i It has been found that the addition of a substantialamount of silicon to aluminum 00 alloys very materially improves theircastiiig qualities, .thus rendering it possible to successfully andeasily make castings which would otherwise e very, diflicult to produce.

,strength of the resulting alloy and as retensile strength may tion fledlprll 38, 1924. Serial No. 709,748.

In particular, the presence of a substantial amount of silicon enablesus to produce alloys having excellent casting qualities, even betterthan those of the well known alloy containing 8 er cent copper, with theuse of only relative y small amounts of copper or-zinc or both. Thepossibility of limiting these heavy metals to amounts of say 5 per centor less in the caseof copper, and 10 per cent or less in the case ofzinc, is very advantageous, both as respects the 05 spects its specificgravit The silicon, by virtue of its lightnem, 0 sets, in a measure, theeflect of the heavy metals, copper and zinc, as well as permitting theuse of the heavier metals in smaller uantities. We have discovered thatthese si icon alloys can be materially-improved by an appro riate heattreatment, which may affect hot the silicon and the heavy-metalconstituents.

The tensile strength of commercially pure cast aluminum is about 12,000pounds per square inch and its elongation about 25 per cent. By addingvarying proportions of hardening metals, particularly copper and zinc,it is possible to increase the tensile strength so that the sand castalloy will have an ultimate strength of nearly 30,000 pounds per s uareinch, but the elongation 1s the by re need to less than 5 per cent. Byaiding a very lar e amount ofzincthe B5 raised to ap roximately 40,000ounds per square inc but the elongation is reduced to almost nothing,and the alloy is very brittle. By casting any of these alloys in a chillmold, the tensile stre h may be increased'in general by approximately5,000 pounds per square inch and the elongation may also be increased.But it has heretofore been impossible to simultaneously produce tensilestrengths of over 30,000 unds per square inch and an elongation o 8 percent or over.

By our method, however, we have been able to extend very greatly therange of the tensile strength and elongation, and of the combination ofthe two, so that we have obtained castings having very much highertensile strengths than those hitherto known in the art, and yetelongations better than those at present obtained with castin alloys 105having only moderate tensile strengt s.

. strength alloys previously knownhave required the presence'ofsubstantial amounts of zinc, even in many cases up to 33 per cent, andhave therefore been considera ly heavier thanpure uminum, while weobtain our results with an addition, in general, of

- lot more than to per cent of total heavier alloying metal or metalsand yet produce a casting which is not only stronger and more ductilebut likewise lighter than would otherwise be obtained.

Various prior investigators have proposed to obtain castinpossessing'the desirable combination of figh tensile strength andductility by heat treatment of a properly made castin but theircontributions to the art have so ar not led to commercially usefulresults. For example, the best results ublished prior to our work arethose of gVilm, who reports having obtained chill castings with atensile strength of about 32,000 pounds per square inch and an elontionof 5 to 7 per cent. More recently fierica and Karr have by heattreatment of an alloy containing 00 per and a large amount of zincobtains a tensile strength of 41,200 pounds per square inch but with anelongation of only 4 per cent. This allo contained about 19 per cent ofheavy allbying metals and hence had a specific 'avity greater than 3.With lighter a]loys,- r example one containing small amounts of copper,magnesium and manganese, they obtained a tensile strength of 35,500pounds per square inch and an elongation of 2.3 per cent. In none of thethree cases men- A tioned above were the properties enough cent copperand 0.2

better than those ssessed by untreated castings to justify t e cost ofthe treatment.

Our invention involves the discovery of important reasons for previouslack' of practical success along-this line, and embraces a combinationof old and new steps so that we are now able by means of our improvedmethod to reduce articles, cast in either sand or molds, having physicalproperties far superior to those of any such castings hitherto produced.B means of our novel method we have r uced sand castin'gs of an aluminumal 0y contain ng 4 per r cent ma esium, ha a tensile strength of about50,000 per square inch and an elon tion of 8.5 per cent, with relativelybig elastic limit; also chilled cast ,having a tensile strength of54,000 un 'per square inch and an elongation o 18 .per cent, with rela-'tively high elastic limit.

This combination of high tensile strength 7 'the castings at t andelongation enables these castings to be used for purposesfor whichaluminum castings have not hitherto been suitable and for which it hasbeen necessary to use the much heavier ferrous materials such as steelor malleable iron. g 2 One example of our process comprises as its firststep the preparation of an aluminum alloy containing about'3 to 5.5 percent copper, preferabl 4 per cent, with no magnesium or' wit magnesiumup to about 0.3 per cent, the iron content in particular eing as low aspossible, preferably not to exceed 0.25 per cent. Iron and silicon arealways present as im urities in aluminum as now obtainable, an a part ofour invention consists in so choosing the raw materials as to limit theiron content of the finished alloy to an amount as low as possible,preferably not over 0.25 per cent. The use of silicon in substantialamounts will be considered hereinafter. 7 w

The ingredients are mixed in the molten state, care being taken to avoidexcessive temperatures at all stages of the melting operation, and themixture is poured'into either a sand mold or a chill mold, and caused tosolidify. After solidification a microscopic examination reveals massesof an aluminum-rich constituentsurrounded by a network of a hard,brittle constitutent, which has been reported to be chiefly CuAl,,. Inthe form of a sand-cast test bar about one-half inch in diameter thealloy has a tensile strength of 18,000 to 25,000 pounds per square'inchwith an elongation of 2.5

to 4 per cent in two inches. A chill cast test bar of the same size has'a tensile strength of about 24,000 to 28,000 pounds per square inch andan elon tion up to 6 per cent in two inches. he iron in the alloy isfound both in the form of needles, reported to be FeAl,, and in adifferent form, apparently as a silicide of iron. The presence of theiron (FeAl,) needles up to a certain amount is beneficial to thestrength and ductility of the alloy in the cast condition, probably dueto the fact that the ordinar path of fracture in the cast allo is throngthe brittle network of anal; which is stren hened by the iron needles.It is foun that these iron needles are very detrimental to the physicalproperties of the casting after the cat treatment discussed below.

The next step in the example of our process now being described consistsinheating the castings to, and maintaining them at,

a temperature of 500 to 540 C. for a period of time depending ulpon theresults esired and themanner in w ich the casting was made. Theprincipal object of heatin e temperature mentioned is to cause theCuAlin the network to go into solution in the solid aluminum-richconstituent. It is found that at the tem oratures"'referred to, thisCuAl, disso ves slowly, in fact surprisingly slowly. In sand castingsthe time necessary for maximum solution of this CuAl may be as much as48 hours, at the temperatures mentioned;

while in chill castin because of thefiner' the freezing int of theeutectic, some of the CuAl, wi remainin the network after heattreatment, and the physical properties of the obtained with will notbeas good ascan be a lower copper content. In

most if not all cases the best combination of physical pro stantially alof the CuAl in the network has been dissolved in the aluminum-richconstituent.

A temperature of heat-treatment high I enough to fuse the eutectic, thatis, the temerature of incipient fusion of the alloy, is

in most cases unfiavorable to the best ultimate results, and it has beenfound that in some instances 540 C. is too high unless the rateof heatinup to that int is very slow or the time o heating be ow that point iscomparatively. long.

A further result of heating the castings at 1 the tem turc mentioned-isto re-dissolve any C 1 which may have'precipitated in small particleswithin the aluminum-rich constituent rather than in the network duringthe previouscooling of the castings,

After the heating period the castings are preferably cooled-rs idly, asb uenching in water. .By the a ve descm procedure, sand castings of analloy containing 4 per cent copper, 0.2 per cent magnesium and less than0.25 per cent iron have been produced within a tensile strength, afteraging,

of about 50,000 pounds per square inch and an elongation of 8.5 percent. Chill castin s have been madeby the same process, of t e samealloy, having a tensile strength of 54,000 pounds per square inch afteraging and an elongation of 18 per cent.

As stated above, quenchi is preferable to slow cooling, but good' resuts can in some. cases be obtained by cooling in a current of air. Amarked difference has been observed between the results obtained bycooling in a current of air and those obtalned by cooling in still air.Even slow cooling, however, produces improvement as compared to the castcondition, not only in the physical properties, but also in resistanceto-corrosion.

The physical properties of castings subjected to t e treatments abovereferred toca-n be further changed by artificial aging, that is, byheating them, immediately after cooltime, one hour being in many casessufii ies results only when submethod, say at a temperature around 520C.

ing, to 'a temperature of 100 to 150 C. for a cient. As a' resu of ;suchheati the tensile strength is increased and the e ongation decreased,and the elastic. limitis inc vei iqlmarkedly.

e method of casting is-an important factor. Thus a method reducing finegrain and improved physio l lproperties, yields castin which are gene ymore amenable to the heat-treatment than does a casting method whichroduees'coarse grain. For example a bar aving a cylindrical test sectiontwo inches lon and a half-inch in diameter, composed o alloy containinabout 4 per cent copper and cast in a sun mold,

has a tensile strength of about 18,000 pounds per square inch andan-elongation of. about 4 per cent. If the bar is heat-treated'by ourfor 24 hours, the tensile strength ma be more than dpubled' (increasingto a ut 37,000 pounds per square inch) and the elongation is increasedto about 12 r cent, or three times its original value. n the other hand,if the bar is cast in such a manner as to cause rapid solidification, saby chill casting in an iron mold, it will ave, after heat-treatment byour method, a tensile strength of about 40,000 oundsper square inch, andan elongation of about 20 per cent.

In sand castings of alloys containing sub-' stantial amounts of silicona considerable portionof the latter appears in the form of relativelylarge lates or needles, and in chill the s' 10011 is found generally insmaller particles, some of which at least are more or less rounded. Theheat-treatment the shape chan and sometimes the. size of the siliconparticles, tending toward'a more 105 rounded form, and the improvementin phys ical properties reduced by the heat-treatment of such change.

The addition to thea-luminum-copper loys, of a small amount ofmagnesium, say 0.2 or 0.3 per cent increases the tensile strength anelastic limit',but is less favorable to'ductility or elon tion.Magnesium may also be added to t e aluminum-silicon alloys, the effect,generally, being to increase the tensile strength and diminish theelongation.

For the best results, our e. erience indicates thatthe iron content 0num copper alloy should be low, but if care is taken to makethecastin'gs by the chill method, a higher ercentage of iron can beused, good results eing obtained with chill castings containing evenmore than 0.4 per cent of iron. Onthe other hand, in the case of heattreated' sand castings, more than thatamount of iron gives lessadvantageous physical properties. The presence of the iron is evidencedby crystalline oys is due in part to this the alumi- 'tai plaice whilethe CuAl, is absorbed into the metal can be heated above the melting p yof the solid-solution crystals of aluminum during heat-treatment. Theiron needles tend to have a beneficial effect on the physical propertiesof the alloy-as cast that is before eat-treatment, but after the luAl inthe network has been dissolved into the aluminum-rich constitutent byheat-treating, the iron needles are a source of weakness, diminishingboth tensile strength and elongation.

' The complete elimination of the iron needles is therefore highlydesirable, but the complete avoidance of iron or even its reductionbelow about 0.25' per cent is not always racticable commercially.However when si icon is resent in excess of the iron the quantity 0lfeAl, formed is lessened, and some of the iron combines with thesilicon to form what appears to be an iron silicide. We have discoveredthat the latter compound freezes in a form less harmful thanthe needlesof FeAl In the case of chill castings, it is found that the FeAl,

needles are much smaller than in the sand castings, and hence. they arenot so objectionable in the heat-treated casting. Since there isconsiderable difliculty in commercially roducing aluminum free from orcontaining less than 0.25 per cent of iron, the desired silicon-ironrelationship is most advantageously obtained by adding silicon whennecessary. For example, if the iron.

content of the aluminum ingot is 0.35 per cent and the silicon 0.3 percent, we nd it advantageous to add about 0.35 per cent silicon. We havealso found that the addition of a small quantity of zinc, say 0.25 percent, improves both the tensile strength and elongation of theheat-treated castings. Chromium up to 0.5 er cent or alittle moreincreases the tensile strength in the heat-treated casting, but reducesthe elontion. With regard to the limits of copper content, we haveobserved that up to about 2 per cent copper, nearly all the CuAl remainsin solution upon solidification, and that beyond 5.5 per cent coppersome of "the (hull, usually remains out of solution even afterheat-treatment. In some cases tfihe 0 nt of the eutectic of CuAl, andaluminum without impairing its physical properties providedthe metal iscooleqL to a temperature slightly below that of complete solidificationand held there for some time before quenching. When substantialpercentages of iron, silicon, magnesium and zinc are present, or any ofthem, the higher permissible temperature is lowered.

A. very important class of alloys embraced by our invention includes theuse of silicon in substantial amount, say from 3 to 15 percent, With thesilicon class of alloys the bestresults are usually obtained when thecastings are made in a chill mold. For example, a chill cast test bar ofan alloy contalnin about 10 per cent silicon and no copper s owed atensile strength around 30,000 pounds per square inch and an elongationof about 7.5 per cent in two inches. After heating at 560 C. for 40hours, followed by quenching, the tensile strength was about 27,500pounds per square inch, but the elongation was found to have beenincreased to 21 able to produce y our method a casting ofaluminum-silicon alloy having great ductility and at the same time atensile stren th twice or more than twice that of aluminum, with thefurther advantage of cod casting qualities as mentioned above. beaddition of copper to this aluminumsilicon alloy increases the tensilestrength enormously but decreases the elongation. Chill cast bars of analloy containing 6 per cent silicon and 4 per cent copper, heated 45hours at 500 to 515 C. followed by quenching, showed a tensile strengthas high as 42,000 pounds per square inch and an elongation of 8 percent. In the high silicon alloys the most advantageous copper content isfrom 2 to 5 per cent. should be noted that the eutectic of thealuminum-silicon system melts at 570 to' 580 'C., which is higher thanthe melting pointof V the aluminum-cop er eutectic which is at 540 C.and there ore it is not only permissible but advantageous to heattreatthe former alloys at higher temperatures-say 530 to 570 C. When copperis, added to the aluminum-silicon alloys a ternary eutectic may formwith a melting point of abou 520 C. and consequently the eat-treatmenttem erature should be lowered accordingly. inc and magnesium also ercent. We are therefore lower the maximum heat-treating temperacent. Incase only silicon and zinc are.

present, it is found that the heat treatment I nuracae has a lessbeneficial effect on the tensile strength, but the elongation is veryfavorably afi'ected. For example, in an alloy containin 8 per centsilicon and 10 per cent zinc, a 0 ill cast test bar gave a. tensilestrength of 29,250 pounds per square inch and an elongation of 4 percent, whereas after. heat treatment the tnsile strength was 30,500pounds per square inch and the elon ation had increased to 11 per cent.It is a so found that the heat-treatment 'can be used in conjunctionwith the process for improving the physical properties of these alloysby the ad ition of alkali metals to the molten allog, as described inthe atent of Junius D. dwards, Francis 0. rary and Han V. Churchill, No.1,410,461,1ssued Mare 21, 1922, on their application Serial No. 426,796,filed November 17, 1920. For example, chill cast test bars of an alloycontaining 8 er cent silicon and 10 er cent zinc, to w ch alkali metalswere added before pouring, gave an average tensilestrength of over41,000 pounds per square inch and an elongation of 6.2 per cent in twoinches. Heat-treatment reduced the tensile strength to 34,000 pounds persquare inch, but increased the elongation to 14 per.

cent.

To obtain the best results it is desirable, in all the above mentionedaluminum-silicon allo s, to keep the iron content low, preferab below0.6 per cent.

It is ound that the coarser the grain reduced in casting, the longermust the heat-treatment be continued to reduce the most beneficial.result's. Accor ingly sand casting with large cross-sectional areasreuire longer heating than chill castings. suall holding at temperaturefor about 7 hours is suflicient for chill castings, whereas 24 hours maybe necessary with sand casts. In addition to the production of asuperior grade of sand castings, permanent 'mold or chill castings(including die castings), the application of our invention is also mostimportant in'connection with the forging and pressing of aluminum allos. If it is desired to roduce a forging o a given sha e, a casting ofsuitable composition, sa per cent copper and 0.2 per cent ma esium, ismade, preferably in a chill mo (1, and 1S subjected to heat-treatment byour method to produce a'starting material for for ing.

In this case, instead of quenchin from the heat treatment temperatureand t en reheatin the article to forging tempewature, we fin itpreferable to simply cool slowly from the heat-treatment temperature tothe forging temperature. The P1866 is then fin-' ished to size under thepresso'r hammer, after which it is given a short heating, say at 520 0.,followed by quenching.

of our method depends, in large measure,

other conditions being the same, upon the degree of improvement desiredin the physica roperties of the casting.

T e essential thing to be kept in mind is the relatively long timereqmred for east alloys in general, as com ared to those rolledaluminum-copper al oys, known to the priorxhcat-treating art. his iscaused, in t e case of the cast copper alloys, by the reater difiicultyin getting the unbroken uAl network into solution in the aluminum, andin the case of the silicon alloys by the slowness of change of form 'ofthe silicon. In case both copper and silicon are prese "in substantialuantities, time must be allowed for both of these changes to take placeto the extent necessary for the desired 1m rovement.

n the copper alloys containing about 4 per cent copper, for example, itis found;

that heating for very long periods, say 48 hours or more, attemperatures only slightly below 500 C. will not, in general, produce asgood results as a. five hour treatment at 520 C. In chill castings ofthe copper alloys it has been found that even two hours heating at 2500. produced sgbstantially as good results as about 22 hours at 500 C. 11order to reduce the time to a minimum, we prefer, if suitabletemperature control is available, to use as high a temperature as can besafely employed without spoiling the castings by overheating.

We have also found that in the case of alloy containing substantialamounts of silicon, the effect upon the silicon particles is producedmore quickly and more completely at relatively high temperatures. Inthese alloys, heating for about 12 hours at 520 C. produces verysubstantial improvement, but the time may be extended, with slightadditional im rovement, if desired. At a temperature 0 550 to 570 C. thealuminum-silicon alloys may be heattreated with more beneficial resultsthan can be produced at 500 C. or thereabouts.

It is; to'be understood that the invention is not limited; to the'specific details herein described but can be practiced in other wayswithout departure-from its spirit.

We claim: v

1. In the art of making aluminum alloy castings, .the method comprisingprepar' an alloy containing substantial amounts 0 silicon and zinc,casting the allo heating thecastingto a temperature slig tlybelow themelting point of the eutectic, and maintaini such temperature until thesilicon partic eshavebeen sufliciently altered to materially improve thephysical properties of the cast alloy.

2. In the art of making aluminum alloy castings, the method comprisingpreparing an, alloy containing substantial amounts of silicon and zinc,casting the allo and causing the silicon therein to take t e form of reatively small particles in the solidfied al- 10y, heating the castin toa tem erature slightly below the melting point 0 the eutectic, andmaintaining such temperature until the silicon particles have beensufliciently altered to materially im rove the physical roperties of thecast al 0y.

3. In t 0 art of making aluminum alloy castings, the method comprisingpreparin an alloy containing substantial amounts 0 silicon and zinc,chill casting; the alloy whereb the silicon is caused to take the form 0relatively small particles in the solidified allo heatin the castin to atern-- perature slightly be 0w the me ting point of the eutectic, andmaintaining such temperature until the silicon particles have beensufliciently altered to materiall improve the physical roperties of thea 0y.

4. In t e art of making aluminum alloy castings, the method comprisingpreparingan alloy containing 3 to 10 per cent silicon and 5 to 15 percent zinc, casting the alloy, heating the casting to a temperatureslight- 1y below the rneltin point. of the eutectic, and maintaining suetemperature until the silicon particles have been sufficiently alteredto materially im rove the physical properties of the cast al 0y.

5. In the art of making aluminum alloy castings, the method comprisingpreparin an alloy? containi substantial amounts 0 silicon, copper anzinc, casting the alloy, heating the casting to a temperature slight lybelow the meltln point of the eutectic, and maintaining sue temperatureuntil the silicon particles have been sufficiently al tered and asuflicient amount of the intergranular copper-rich constituent has beendissolved to materially improve the physical properties of the castalloy.

, silicon,

6. In the art of making aluminum alloy castings, the method comprisingpreparin an alloy containi substantial amounts 0 silicon, copper anzinc, casting the alloy, and causing the silicon therein to take the ormof relatively small particles in the solidified allo heating the castingto a temperature slig tly below the melting point of; the eutectic, andmaintaining such tem perature until the silicon particles have beensufficiently altered-and a suflicient amount of the inter-granularcopper-rich constituent has been dissolved to materially improve thephysical roperties of: thecast alloy.

7. In e art of aluminum alloy castings, the method comprising preparingan alloy containing substantial amounts 0 copper an zinc, casting thealloy, heating the casti at a temperature slightlybelow the'meltinguntilthe silicon particles have been sulfian alloy containin point of theeutectic all ciently altered and a suflieient amount of theinter-granular copper-rich constituent has been dissolved to materiallyim rove the physical properties of the cast loy, and cooling the castinrapidly.

S. In the art 0 making aluminum alloy castings, the method comprisingpreparing substantial amounts 0 silicon, copper an zinc, casting thealloy and causing the silicon therein to take the form of relativelysmall' articles in the solidified "alloy, heati e casting at atemperature slightly low the melting point? of the eutectic until thesilicon particles have been sufliciently altered anda sufficient amountof the inter-granular copperrich constituent has been dissolved tomaterially improve thel hysical properties of the cast alloy, andcooling the casting rapidly.

9. In the art of making aluminum alloy castings, thegmethod com risingpreparing an ,alloy containing 3 to 1 per cent silicon, 2 to 5.5 {percent copper, and 5 to 15 er cent zinc approximately, casting the al oy,heating the casti to a temperature slight ly below the melti point ofthe eutectic, and maintaining suc temperature until the siliconparticles have been siliciently altered and a sullicient amount of theinterranular copper-rich constituent has been ties of the cast al 0?. p

10. In the art 0 making aluminum alloy castings, the method comprisingpreparing an alloy containing substantial amounts of issolved tomaterially rove the physical proper the cast a 0y, and cooling thecasting rapidly.

11. In the art of making aluminum alloy castings, the method comprisingpreparing an alloy containing 3 to 10 per cent silicon, 2 to 5.5 percent copper, and 5 to 15 er cent zinc, approximately, casting the al oyand causing the silicon therein to take the form of relatively smallparticles in the solidified alloy, heating the casting to a temperatureslightly below the meltin point of the eutectic, and maintaining suchtemperature until the silicon articles have been sufliciently altered ana sufficient amount of the inter-granular copper-rich constituent hasbeen dissolved to. materially improve the physical properties of thecast 0y. 12. In the art of making aluminum alloy castings, the methodcomprising preparing an alloy containiiw substantial amounts of silicon,copper an zinc, casting the alloy, heating the casting to a temperatureslightly below the melting point of. the eutectic, maintaining suchtemperature until the silicon particles have been sufficiently alteredand a sufliuent amount of the inter-granular coppei rich constituent hasbeen dissolved to materially improve the physical properties of the castalloy, and rel-heating the casting at a relatively low temperature toincrease the tensile strength of the alloy.

13. In the art of making aluminum alloy castings, the method comprisingpreparing an alloy containing substantial amounts 0 silicon, copper andzinc, casting the alloy and causing the silicon therein to take form ofrelativley small particles in the solidified alloy, heating the castingat a tern Jerature slightly below the melting point 0 the eutectic untilthe silicon particles have been sufliciently altered and a sullicientamount of the inter-granular copper-rich constituent has been dissolvedto materially improve the physical properties of the cast alloy, coolingthe casting rapidly, and reheating the casting at a relatively lowtemperature to increase the tensile strength of the alloy ,14. As a newarticle of manufacture, a heat-treated casting of an aluminum alloycontaining zinc,'and containing silicon in amount between 3 and 15 percent, characterized by the silicon being in the form of small finelydispersed more or less rounded particles and substantially devoid oflarge plates and needles of silicon, withconsequent high tensilestrength and elongation.

15. As a new article of manufacture, a heat-treated castin of analuminum alloy containing zinc an substantial amounts of silicon andcopper, characterized by the silicon befiig in the form of a smallfinely dispersed more or less rounded particles and substantially devoidof large ,silicon plates or needles and of undissolved inter-granularcopper-rich constituent, with consequent high'tensile strength andelongation.

16. As a new article of manufacture, a

heat-treated casting of an aluminum alloy containing zinc and siliconand a substantial amount of copper, and having a low iron content,characterized by the substantial absence of undissolved inter-granularcopperrich constituent, and having high tensile strength and elongation.

17. As a new article of manufacture, a heat-treated casting of analuminum alloy containing zinc and 3 to 15 per cent silicon, containingbetween about 2 and 5.5 per cent of copper, and havinga low ironcontent; characterized by the silicon being in the form of small finelydispersed moreor less rounded particles and substantially devoid oflarge plates and needles of silicon, with consequent high tensilestrength and elongation.

18. As a new article of manufacture, a heat-treated and artificiallyaged casting of an aluminum alloy containing zinc and substantiallyamounts of silicon and copper, characterized by the silicon being in theform of small finely dispersed more or less rounded particles andsubstantially devoi of large silicon plates or needles and ofundissolved inter-granular copper-rich constituent, with consequent hightensile strength and elongation. I

In testimony whereof we hereto afiix our signatures. ZAY J EFFRIES.

ROBERT S. ARCHER.

and causing comprising preparing an alloy containiiw substantial amountsof silicon, copper ant zinc, casting the alloy, heating the casting to atemperature slightly below the melting point of the eutectic,maintaining such temperature until the silicon particles have beensufiiciently altered and a sufi'nlent amount of the inter-granularcopper rich constituent has been dissolved to materially improve thephysical properties of the cast alloy, and re-heating the casting at arelatively low temperature to increase the tensile strength of thealloy.

13, In the art of making aluminum alloy castings, the method comprisingpreparing an alloy containing substantial amounts of silicon, copper andzinc, casting the alloy the silicon therein to take form of relativleysmall particles in the solidified allo heating the casting at atemperature slig tly below the melting point of the eutectic until thesilicon particles have been sufliciently altered and a suilicient amountof the inter-granular copper-rich constituent has been dissolved tomaterially improve the physical properties of the cast alloy, coolingthe casting rapidly, and reheating the casting at a. relatively lowtemperature to increase the tensile strength of the alloy ,14. As a newarticle of manufacture, a heattreated casting of an aluminum alloycontaining zinc,'and containing silicon in amount between 3 and 15 percent, characterized by the silicon being in the form of small finelydispersed more or less rounded particles and substantially devoid oflarge plates anl needles of silicon, withleonsequent high tensilestrength and elongation.

15. As a new article of manufacture, a heat-treated casting of analuminum alloy containing zinc and substantial amounts of castings, themethod siliconpnd copper, characterized by the silicon being in the formof a small finely dispersed more or less rounded particles andsubstantially devoid of large ,silicon plates or needles and ofundissolved inter-granu lar copper-rich constituent, with consequenthightensile strength and elongation.

16. As a new article of manufacture, a heat-treated casting containingzinc and silicon and a substantial amount of copper, and having a lowiron content, characterized by the substantial absence of undissolvedinter-granular copperrieh constituent, and having high tensile strengthand elongation.

17. As a new article of manufacture, a heat-treated casting of analuminum alloy containing zinc and 3 to 15 per cent silicon, containingbetween about 2 and 5.5 per cent of copper, and having a low ironcontent; characterized by the silicon being in the form of small finelydispersed moreor less rounded particles and substantially devoid oflarge plates and needles of silicon, with consequent high tensilestrength and elongation.

18. As a new article of manufacture, a heat-treated and artificiallyaged casting of an aluminum alloy containing zinc and substantiallyamounts of silicon and copper, characterized by the silicon being in theform of small finely dispersed more or less rounded particles andsubstantially devoid of large silicon plates or needles and ofundissolved inter-granular copperich constituent, with consequent hightensile strength and elongation.

In testimony whereof we hereto affix our signatures.

ZAY J EFFRIES. ROBERT S. ARCHER.

Certificate of Correction.

' t is hereby 192 on the a )lication of Zay'Jeffries of Lakewood,

appear in the printed specification requiring T Gambian-$37, 19930.;same page,

9, for the mispelled word for November 17, 1920 read A 02 read 520; page6, line 94, ,auficiently; page 7, line 43, cla

a same page, line and that the said the same may conform Signed andsealed this 9th day of ifsmu] to the record of 5, after the wen? 71,claim 18, for the Word Letters Patent should be read the case inMarch,'A. D. 1926.

certified that in Letters Patent No. 1,572,488, granted February 9,

of Shaker Heights and in, for an improvement in Aluminum-ilicon Alloys,errors Robert S. Archer,

correction as follows: Page 5, line 19, line, 94, for 250 Sfiicientlyread 8* of strike out/the article antially read substantial; with thesecorrections therein that the Patent Olfice.

M. J. MOORE, Actmg of Patents.

.sufziciemly; page 7, line 43, ch

Certificate of Correction.

It is hereby certified that in Letters Patent No. 1,572,488, grantedFebruary 9, 1926qgpn the a plication of Zay'Jeffries, of Shaker Heights,and Robert S. Archer, of Lakewood, hio, for an improvement inAluminum-Silicon Alloys, errors appear in the printed specificationrequiring correction as follows: Page 5, line 19, for November 17, 1920read N mbei' i', 7990.; same page, line, 94, for 250 read 520; page 6,line 94, 9, {or the mis elled word sificiently read 5, after the ofstrike out the article a same page, line 71, claim 18, for the word slit'antially read substantzhl; and that the said Letters Patent should beread with these corrections therein that the same may conform to therecord of the case in the Patent Oflice.

Signed and sealed this 9th day of 1\[arch,'A. D. 1926.

issue] M. J. MOORE,

Acting of Patents.

